1. Field of the Invention
This invention relates to pneumatic off-the-road tires, and more particularly to an improvement in the running performance of the pneumatic off-the-road tires used in motocross racing of running motorcycles on rough roads consisting of soft and hard road surfaces.
2. Related Art Statement
Heretofore, a tire as shown in FIG. 6 has been known as the pneumatic off-the-road tire. In FIG. 6, numeral 1 is a pneumatic off-the-road tire used in motocross racing, which has a tread pattern dividing a surface portion 2a of a tread 2 by grooves 3 into many isolated blocks 5. The size and arrangement of the block 5 are determined considering straight running road and cornering road in the racing course, the state of road surface and the like. In the conventional pneumatic off-the-road tires, blocks 5A arranged in a central portion 2b of the tread 2 attach importance to traction performance, so that blocks 5 with an edge 5a extending in the widthwise direction of the tire are fundamentally arranged in the central portion 2b. Thus, traction performance against momentary torque is obtained during straight running.
However, when the pneumatic off-the-road tire 1 is run on a circuit course for motocross racing, the motorcycle runs not only on the straight running road but also on the cornering road while being largely inclined at a large camber angle in both left and right directions. In this case, the tread 2 of the tire 1 shifts its ground contact area from the central portion 2b to both side portions 2c to thereby generate a large lateral force in the lateral direction. In the tread pattern as shown in FIG. 6, there is a problem in that the shifting of the ground contact area from the central portion 2b to the side portion 2c does not exhibit gentle behavior. That is, in the conventional tire 1, it is difficult to simultaneously establish traction performance and shifting performance, so that the driver is required to have a special driving technique in running on the cornering road.